Project Summary Deaths from suicide continue to be a major public health concern, particularly among youth and young adults, for whom suicide ranks as the second leading cause of death. Despite growing research on suicide, knowledge about the proximal behavioral and psychosocial mechanisms that facilitate the development of suicidal thinking and/or the transition to suicidal behavior. Nonsuicidal self-injury (NSSI) is the intentional destruction of body tissue without suicidal intent, typically cutting or burning the skin, and has been identified as a particularly robust risk factor for suicide. Studies find that up to 19% of college students report engaging in NSSI during their college years, placing many at elevated risk for suicide. Remarkably little is known about the temporal course of NSSI and suicide ideation/ behavior, or about why and how NSSI confers its risk for suicide. The proposed study aims to fill these knowledge gaps through an 18-month longitudinal study of self-injuring college students. Using the integrative motivational- volitional theory of suicide as a guide, the current study proposes that the behavioral severity of NSSI, lack of effectiveness of the NSSI in achieving coping functions, and self-identification with NSSI are mechanisms contributing to the development of suicidal ideation. Whereas, habituation to pain and fearlessness about death, attentional bias towards self-injury, and impulsively engaging in NSSI are mechanisms mediating the transition from NSSI to suicide behavior. College students reporting current NSSI will be recruited to complete behavioral-reaction time tasks and self-report measures of the study variables within a laboratory setting at baseline, 6-, 12-, and 18-months post baseline. Latent growth modeling will be used to examine how the proposed NSSI mechanisms mediate changes in suicidal ideation and attempts over time. The results will provide essential information to the field of suicide prevention, and have the potential to significantly impact clinical practice by identifying specific mechanisms and markers of suicide risk that can be translated into assessment and intervention strategies.